Charge-transporting thin films consisting of organic compounds are used as light-emitting layers and charge-injecting layers in organic electroluminescent (EL) devices. In particular, a hole-injecting layer is responsible for transferring charge between an anode and a hole-transporting layer or a light-emitting layer, and thus serves an important function in achieving low-voltage driving and high brightness in organic EL devices.
Processes for forming the hole-injecting layer are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. Comparing these different processes, wet processes are better able to efficiently produce thin films having a high flatness over a large area. Hence, with the progress currently underway toward larger-area organic EL displays, there exists a desire for a hole-injecting layer that can be formed by a wet process.
In view of these circumstances, the inventors have developed charge-transporting materials which can be employed in various wet processes and which moreover give thin films that, when used as hole-injecting layers for organic EL devices, are capable of achieving excellent EL device characteristics. The inventors have also developed compounds which have a good solubility in organic solvents used in such charge-transporting materials (see, for example, Patent Documents 1 to 4).